Introduction Pure Struma ovarii (SO) constitute 5% of all mature cystic teratomas of the ovary (MCT). Malignant transformation of struma ovarii (MSO) though rare, occurs in merely 0.1% of all MCT. Recently, recurrence was also reported in a case of proliferative struma but there is a paucity of literature on the molecular basis of this occurrence. Our objective was to study the clinicopathological profile of Struma ovarii cases and to identify the molecular basis of MSO and Proliferative struma cases.

Methods This was a retrospective study conducted for the past 9 years (2015 to 2023). All cases with confirmed histopathological diagnosis of struma ovarii were reviewed and clinicopathological profiles were noted from the archives. In MSO and a case of proliferative struma, IHC and RT-PCR was done to identify the molecular profile of these cases.

Results We received a total of 30 cases of pure struma ovarii. 5/30 cases were malignant while the rest were benign. The average age of presentation was 37 years for benign SO and 40 years for MSO. Cases of MSO comprised of 1 PDCA, 2 FVPTC, 2 strumal carcinoids and 1 case of proliferative struma were noted. While RTPCR revealed NRAS positivity in both FVPTC cases, BRAF NRAS was negative in the case of proliferative struma.

Conclusion/Implications The average age of MSO presentation is 40 years. Struma cases with large cystic adnexal masses may have ascites and raised CA 125 levels, mimicking malignancy clinicoradiologically. Though thyroid carcinoma in Struma shows similar molecular abnormalities as its thyroid counterpart, proliferative struma does not harbour BRAF/NRAS mutations.